1. Field of the Invention
The present invention relates to a polyurethane foam and to a process for production thereof. More particularly, the present invention relates to a polyurethane foam, inter alia, having superior energy absorbance, efficiency and other improved properties compared to prior art polyurethane foams.
2. Description of the Prior Art
It is known in the art that polyurethane foams have energy absorbing properties. Thus, heretofore, such foams have been used in helmets, shoe insoles, furniture, seating applications and the like. These foams have also found widespread use in vehicular applications such as door panels, knee bolsters, air bag doors, headliners, bumpers, instrument panels, sun visors and other areas of the vehicle intended to absorb energy upon impact.
Known energy absorbing polyurethane foams can be divided generally into two groups: recoverable foams and crushable foams.
Recoverable foams are generally resilient in nature and will recover in response to repeated impact with little or no loss in memory. The principal advantage of these foams is that they do not need to be replaced after impact. However, in order to gain this advantage, it is necessary to compromise properties such as energy absorption and efficiency, and thus,it is generally accepted that these foams have a reduced energy absorption and efficiency.
Crushable foams are generally rigid and will permanently crush and/or disintegrate in response to an impact. Energy absorption occurs as a result of damage to the cell structure of the foam during impact. See, for example, U.S. Pat. Nos. 5,143,941 and 5,167,884 (both to Rossio etal.), the contents of each of which is hereby incorporated by reference. The principal advantage of these foams is that they possess relatively high energy absorption and efficiency. However, a disadvantage of these foams is that they need to be replaced after impact due to the internal damage to the foam resulting from impact. Another significant, yet generally unreported, disadvantage of these foams is that the force or compressive loads that they can endure are relatively independent of impact velocity. Consider, for example, a particular crushable foam which is designed to absorb the energy of a compressive force of 28 p.s.i. at a deflection (relative penetration depth) of 50% and an impact velocity of 15 m.p.h. If the impact velocity is decreased, the compressive force is substantially unchanged and the result is a foam that feels harder on impact leading to potentially dangerous consequences for a passenger in the vehicle. If the impact velocity is increased, there is an increased likelihood that the foam will fail since it was designed to absorb energy at a lower impact velocity.
In in the 1995 Edition of "EMERGING ISSUES IN MOTOR VEHICLE PRODUCT LIABILITY LITIGATION" by the American Bar Association, Section of Tort and Insurance Practice Committee on Automobile Law, Chapter C thereof is a paper entitled "Some Considerations Relating to Side Impact Occupant Protection and Compliance with FMVSS 214" by Geoffrey J. Germane, Ph.D. In this paper, the contents of which are hereby incorporated by reference, Dr. Germane, inter alia, states:
"Padding concepts have been studied for decades using sled tests, crash tests, other laboratory tests and mathematical models in an attempt to determine optimum pad characteristics and placement for dummy acceleration reduction. Numerous padding materials and configurations have been researched resulting in greater understanding of the tradeoffs between energy absorption, stiffness, and expected injury levels in side impacts at various velocities. Padding designed to optimize energy absorption could increase low speed injury due to relatively high compression forces. The ideal pad, with compression forces proportional to compression speed gives lowest relative forces levels over the widest range in contact speeds. Such padding is not presently available as a homogeneous material. Simulations of ideal pad characteristics with mechanical systems are theoretically possible but would not be practical for production vehicles even if reliable examples could be built." (emphasis added)
Dr. Germane's paper is instructive since it describes the state of the art (the paper was presented in March 1995) and it indicates that, notwithstanding prior art energy absorbing padding (including polyurethane foams), for all practical purposes there does not exist a material which is capable of absorbing compressive forces directly proportional to impact or compression velocity.
In light of these difficulties in the prior art, it would be advantageous to have a polyurethane foam having improved energy absorbing properties, including: recoverability, relatively high energy absorbance and efficiency, and the capability of absorbing compressive forces directly proportional to impact or compression velocity.